Electrostatic recording apparatus



, Jan. 15, 1957 McNANEY 2,777,745

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Joseph T Mc/Vmeq BY ATTORNEY Jan. 15, 1957 J, T, MONANEY 2,777,745

ELECTROSTATIC RECORDING APPARATUS Filed Oct. 4, 1952 3 Sheets-Sheet 3 zou. 0F

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75 BAD/1k RECEIVER m K Q \I 2 0 m 3 INVENTOR: J05 e Jh T Mc Naney United States Patent 6 l 2,777,745 ELECTROSTATIC RECORDING APPARATUS Joseph T. McNaney, San Diego, Calif... assignor, by mesne assignments, to General Dynamics Corporation, a corporation of Delaware Application October 4, 1952, Serial No. 313,167 9 Claims. (Cl. 346-74) This invention relates to recording apparatus and particularly to apparatus for recording intelligence projected on the screen of a cathode-ray tube.

The recording apparatus of my invention is particularly suitable for providing a record of intelligence which is represented by electric signals. By way of example, the apparatus may be employed as a high-speed printer for recording information represented by code signals on punched or magnetic tapes.

The apparatus is also suitable for providing permanent visible records of information which is produced on the screen of a cathode-ray type tube during selected intervals of time.

The invention contemplates the use of a cathode-ray vacuum tube having a screen or target area comprising a mosaic of electrically capacitative elements. An electrically capacitative generally plate-like element is disposed outside of the tube, in juxtaposition to and spaced form the target area. A source of potential is connected to the source of electrons within the tube, that is, the cathode, and to the capacitative plate. By this means, when the cathode is energized to direct a beam of electrons on the mosaic inner surface of the cathode-ray tube, a difference in potential is established between the target area and the capacitative plate element over the area of the mosaic upon which the electron beam impinges, the size and shape of the area corresponding to those characteristics of the electron beam, and the difference in potential being dependent upon the magnitude of the impressed potential. For recording from this arrangement, a preferably thin and flexible non-conductive and polarizable material is interposed between the tube and the capacitative plate element as a recording medium. By this means an electrostatic record of the intelligence developed in the cathode-ray tube is produced on the recording medium.

When employed as a printer for alphabetical or numerical information, the cathode-ray tube of the present invention is provided with means for shaping the crosssection of the electron beam in the form of characters.

In one embodiment of the invention, the intelligence is first electrostatically recorded on the recording medium, and then the electrostatic record is converted into a visible record. A dry printing process may be employed to provide a permanent record of the information. One preferred form of screen for the tube usedin this embodiment is formed by providing the inner surface of the target area of the tube with a mosaic of secondary emissive material.

In another embodiment of the invention, the intelligence is recorded directly on a recording medium which changes in color when electric current passes through it. In this embodiment, a plurality of closely spaced conductors which extend through the target area of the tube are employed as the screen of the cathode-ray tube.

The invention is explained with reference to the drawings, in which:

Fig. 1 is a simplified illustration of the recording apparatus;

Fig. 2 illustrates the interior surface of one form of target area which may be employed in the cathode-ray tube of Fig. 1;

Fig. 3 shows another type of target area or screen which may be employed in the tube of Fig. 1;

2,777,745 Patented Jan. 15, 195'? EQQ Fig. 4 shows an enlarged portion in cross-section of the target area shown in Fig. 3;

Figs. 5, 6 and 7 show three recording arrangements for providing a printed record of intelligence; and

Fig. 8 illustrates a recording arrangement for providing a record of intelligence developed on the screen of a cathode-ray tube in a radar receiver.

The recording arrangement shown in Fig. 1 is a simplified illustration of the principles of the invention. A cathode-ray tube 12 serves to convert the intelligence to be recorded from electrical impulses into suitable form to provide a permanent and readable record. The tube of Fig. l is of a conventional type except that it is provided at one end with a screen or target area 13 which is substantially flat so as to accommodate a flat recording medium 26 in contact with or nearly in contact with its outer surface. Preferably an intensifier anode 14 of a conventional type is employed in the tube.

A conventional source 16 of high voltage and a voltage divider 18 provide suitable focusing and accelerating potentials of the electron beam of the tube.

The intensity of the beam of electrons in the cathoderay tube and its position on the screen or target area 13 is controlled by a source 20 of control signals which may be of any desired type.

An electrically capacitative plate member 22 is disposed in juxtaposition to and slightly spaced from the outer surface of the target area or screen 13 and is substantially parallel thereto.

Fig. 2 is a cross-section of the tube 12 looking toward the target area illustrating a construction in which the inner surface of the target area or screen 13 is coated with a secondary-emissive substance, such as aluminum oxide, in such a manner that the particles of the second ary-emissive materials are separated and insulated from each other to form a mosaic structure, each serving as an individual electrocapacitative cell. Since the material is of a secondary-emissive character, the electrostatic charges in each particle do not accumulate but are only energized during the time the electron beam of the gun is impinged against them. Preferably the glass forming the target area 13 of the tube 12 is thin with respect to the thickness of the walls of the tube in order to minimize the fringing efiect of the electrical fields passing through it.

Fig. 3 illustrates another form of suitable screen 13 in which the target area comprises a plurality of closely spaced conductors 30 Which are electrically insulated from each other and extend from the inner surface of the glass forming the screen 13 of the tube to its outer surface, as shown in detail in Fig. 4, thus providing a mosaic of elements serving to conduct electrical energy from within the evacuated tube to the outer surface of its screen. This embodiment of the screen 13 has the advantage that the conductive path from the negative terminal of the source 24 is extended to the outer surface of the target area of the tube 12, thereby minimizing the effect of stray electrostatic fields in passing through the glass wall of the tube.

The invention contemplates the use of a recording medium 26 adapted to be disposed between the outer surface of the target area 13 and the plate member 22, to provide a permanent record of the intensity, movement, and shape of the electron beam Within the tube 12.

The recording medium 26 is preferably thin, flexible, and has high insulating properties. It will be noted that the system comprising the target area 13 of the tube 12, the plate member 22, and the recording member 26 forms a condenser, with the latter element serving as the dielectric.

A potential developed between the plate member 22 through the source 24, to the cathode 25 and any portion of the target area 13 energized by the resulting electron beam will polarize or create an electrostatic stress on the recording medium 26 when interposed therebetween thus providing an electrostatic recordcorresponding to the intensity, and shape of the electron beam'and to the location of its impingement against the target area. Those portions of the recording medium 26 that are,not exposed between the plate member 26 and the energized portion of the target area 13, remain unpolarized and form a field" for the images produced by the polarized regions.

The definition of the polarized images produced in the above manner from the unpolarized field requires a minimization of the air gaps on either side of the recording medium 26 between the plate'member 22 and the face of the tube 12, and therefore the plate member 22 is preferably spaced from the tube only as much as practically necessary to permit the interposition and movement of the recording medium 26.

When intelligence is to be recorded electrostatically by the arrangement of Fig. 1, it ispreferable that the member 26 be electrostatically polarized before it is positioned between the plate member 22 and the target area of the tube 12. The initial charge on the recording member 26 should be opposite in polarity to that of the images which are electrostatically developed so that the polarization of the areas of the member 26 in which the images are recorded is reversed from the field by the charge applied through the beam of the cathode-ray tube 12.

In the embodiment of the invention utilizing a tube having a target area 13 of the type shown in Figs. 3 and 4, the recording medium 26 may be a current-sensitive paper which changes in color when an electrical current ispassed through it. In this case, the potential built up from the source 24 between the plate member 22 and the energized portion of the target area 13 is sufficient to break down the dielectric recording member 26, and

produce a visible image by its discoloration, of the same shape as that of the electron beam and corresponding to its location on the target area 13.

Thus, when a screen of the type shown in Figs. 3 and 4 is employed, the recording medium 26 may be either a current-sensitive paper which provides a direct record of the images which are projected on the target area of the tube, or it may bean electrostatically polarizable member which provides an electrostatic record of the images. In the latter case and in the case in which a target area of the type described in connection with Fig. 2 is employed, the electrostatic record may be converted to a visible record by a suitable electrostatically charged powder over the surface of the'recording member 26. The powder should be of a contrasting-color to the recording member 26. The powder is preferably charged so that it will adhere to the electrostatically charged image areas and it will fall 01f or be repelled from the uncharged field areas.

By properly proportioning the electrostatic charges on the member 26 and the charge on the electroscopic powder, an indication of the relative intensity of the images which are projected on the screen of the tube may be obtained.

The recording arrangement shown and described in connection with Fig.1 may be employed in various manners, as illustrated in the arrangements shown in Figs. 5 to 8.

Fig. 5 shows an electrostatic recording arrangement employed in conjunction with dry printing means for providing a printed record of alphabetic and numeric information at high speeds.

The cathode-ray tube 32 is provided with means for shaping the cross-section of the electron beam in the form of alphabetic or numeric characters which are to be printed. The tube is of the general type disclosed in my U. S. Patents Nos. 2,275,017 and 2,283,383, and in my co-pending applications Serial No. 297,480, filed July 7, 1952 and Serial No. 298,603, filed July 12, 1952. The target area or screen 33 of the tube 32 may be any of the types described above with reference to Fig. 1, and it is preferably curved so as to conform to recording arrangement mounted on a rotatable drum 4.0.

The tube 32 is provided with a thin matrix 34 disposed perpendicularly with respect to the path of the electron beam of the tube. The matrix 34 is a solid member provided with apertures shaped like the characters to be printed. Openings shaped in the form of the numbers one to nine are shown in Fig. 5 in order to illustrate the invention. The letters of the alphabet and some punctuation marks may also be provided.

A set of selection plates 36 is'provided for selectively directing the electron beam of the tube through the apertures in the matrix 34, and a set of deflection plates 38 is provided for positioning the electron beam after it traverses the matrix. Thus, the selection plates 36 serve to select the respectivecharacters which are to be printed, and the deflection plates 38 serve to cont'rolthe position or orientation of the characters on the screen or target area 33 of the tube 32.

A source 39 of control signals serves to provide the signals required for gating and positioning the electron beam of the tube. By way of example, the source 39 of control signals may be a circuit for converting binary code signals to suitable potentials for controlling the electron beam of the tube. One such arrangement is disclosed in my co-pending application Serial No. 340,240, filed March 4, 1953.

The electrostatic recording apparatus comprises a conductive drum 4 0 which is provided with a thin coating of electrostatically polarizable. material 42-, say polystyrene, on its outer surface. The drum A) may be rotated continuously or in steps if desired. Preferably the movement of the drum is synchronized with the control signals which are provided by the source 39 so that information may be recorded along straight lines. The shaft of the drum 49 is connected to the conductive portion of the drum 40 and through a brush 44 to ground.

As shown in Fig. 5, the drum 40 is intended for clockwise rotation. An electrode 46 extends across the drum 40 adjacent the outer polarizable coating 2 on the portion of the drum advancing towards the position of the tube 32, and is connected to one side of a source 48 of high potential, serving to apply an electrostatic charge to the polarizable outer surface 42 of the drum 40.

In the arrangement of-Fig. 5, the tube 32 functions identically to the tube 12 of the arrangement shown in Fig. l, and is provided with the equivalent elements 14, 16, 18 and 24,. In the present instance, the source of high potential 24 is electrically connected to the portion of the drum 40 juxtaposed to the target area 33 of the tube 32 through ground and the brush 44, so that the latter serves' as the electrically capacitative plate member 22 of the'arrangement of Fig. 1.

As the polarized outer surface 42 is moved into position opposite the target area 33, electrostatic images are produced on its outer surface in correspondence with the intensity, shape, and location of the electron beam of the tube 32, the polarity of the image portions being opposite in sign to that of. the polarized surface 42 forming the field or background.

A receptacle 49 and agitators 50 serve to cause particles of suitably charged electroscopic powder 51 to impinge upon the member 42 as the drum rotates. The powder may be charged so that it is attractedand adheres to the image areas and is repelled by the oppositely charged background areas or vice versa. Thus, the electroscopic powder produces a visible record of the images which are electrostatically recorded on the member 42. i i

'The images formed by the electroscopic powder are transferred to paper 52 which ism'oved in synchronism with the drum 4%. An electrode 54, which is connected to a source 56 of high voltage, serves to apply an electrostatic charge to the paper 52. The charge is of opposite polarity to that of the powder onthe image areas of the member 42 and of sufficient intensity so that the powder is attracted and the images are transferred from the member 42 to the paper.

The electroscopic powder 51 is fusible or thermoadhesive and a heater 58 is provided for causing the powder images to be aifixed to the paper so as to provide a permanent printed record of the images. One suitable powder for the purpose is formed of carnauba wax with .a coloring material. In the alternative, the paper may be provided with a thermo-adhesive coating so that sub stantially any powder will adhere to it when it is heated.

A cleaning brush 60 is provided for removing surplus powder from the drum after each transfer operation.

In operation, the drum 40 is moved in synchronism with the intelligence which is projected onto the screen 33 of the tube 32 so that the images are recorded at predetermined positions along the drum. The images to be printed are recorded electrostatically on the polarizable material 42 by the charge which is applied from the source 24 of high voltage through the shaded electron beam of the cathode-ray tube 32.

As the electrostatically recorded images pass the receptacle 49, the electroscopic powder 51 adheres to the charged image areas, and as thepowder images pass the electrode 54 they are transferred to the recording paper 52 which provides a permanent record of the information.

The arrangement shown in Fig. 6 is similar to that shown and described in connection with Fig. 5, but in this embodiment, the electrostatic images are developed directly on the recording media which is then processed to form a permanent record. For this purpose, the polarizable outer covering of the drum 40 is replaced with a thin, flexible, recording media 64 which is preferably continuously fed over the drum 4% and between the target area of the tube 32 from a roll and by a suitable feed mechanism. The recording media 64, by way of example, may be a paper impregnated with polystyrene resin, or wax to produce a high dielectric constant.

Electrostatic images are produced on the continuously moving media 64 from the target area of the cathoderay tube as the media is moved by it, and the exposed media is then passed over the receptacle 49 so as to produce visible images of the electrostatically recorded images by the adherence of the electroscopic powder. The media 64 is then passed over the heater 58 which causes the powder images to fuse into or adhere to the paper and form a permanent record of the intelligence.

The arrangement shown in Fig. 7 employs a currentsensitive material 70 for permanently recording the images which are produced on the target area of the cathode-ray tube 32. The material 70 employed in this embodiment of the invention is of a type which changes in color when an electric current is passed through it. It is necessary to provide a target area of the type shown and described in connection with Figs. 3 and 4 for the cathode-ray tube 32 in order to provide a conductive path through the envelope of the tube 32 and permit a breakdown of the dielectric represented by the material 70 and a passage of high voltage current between the target area of the tube 32 and the drum 4t). If desired, the conductive wires forming the target area may be extended from the face of the screen so as to make positive electrical contact with the paper '70.

Since the intelligence which is produced on the screen of the cathode-ray tube 32 is recorded directly on the paper '70 by the current which flows from the source 24 to the conductive drum 40, no further processing of the paper is required.

Fig. 8 illustrates a recording arrangement for providing a visible record of intelligence which is projected onto the screen of a cathode-ray tube in a radar receiver. In this embodiment of the invention the cathode-ray tube 74 is a type which is suitable for projecting radar displays on the target area of the tube. The target area, however, is constructed in accordance with arrangement heretofore described in connection with Figs. 1 and 2.

A rotatable magnetic deflection coil 76 and a radar receiver '78 for controlling the electron beam of the tube are shown in block diagrammatic form. The magnetic deflection coil '76 and the radar receiver 78 may be conventional types for providing PPI type displays on the target area of the tube 74.

As in the case of Fig. 1 arrangement, an electrically capacitative plate 22 is located in juxtaposition with and slightly spaced from the outer surface of the target area of the tube 74.

It is preferable that the screen of the cathode-ray tube 74 be substantially flat so that a recording medium 7 8 can be passed between the face of the tube 74 and the plate member 22.

In this embodiment of the invention a thin, flexible polarizable member 78 in the form of a continuous belt is employed to provide an electrostatic record of the intelligence which is produced on the target area of the cathoderay tube 74. The belt '78 should be composed of a transparent or translucent material. A crank 80 is shown for moving the belt 78, representing means for continuously feeding the belt 73 across the face of the tube 74 and through the succeeding apparatus.

A portion of the belt '78 is initially polarized by means of a source 48 of high voltage and a pair of spaced electrodes 46, 82. Then the polarized portion of the belt '73 is positioned between the target area of the cathode-ray tube 74 and the plate member 22. A switch 34 is closed to cause the beam of the cathode-ray tube to reverse the charge in the belt 78 as heretofore described, and in accordance with the intelligence which is produced on the screen of the tube during the period while the switch is closed. The switch 84 is then opened and the portion of the belt on which the electrostatic images are recorded is passed over the receptacle 49 where properly charged electroscopie powder 51 is deposited on the image areas. The portion of the belt which carries the powder images is then positioned over a ground glass screen 88 which is illuminated by a lamp 99. The images thus can be visually observed while the belt is in this position, and thereafter the information may be transferred to a printed record by moving the belt '78 between the electrodes 54 and 92 which causes the electroscopic powder to be transferred to the paper 52. The continuously-fed paper 52, which is synchronously moved with the belt 7 8'by suitable drive means, is then passed over a heater 53 which fuses the powder 51 and forms a permanent record as heretofore described. A cleaning wheel 60 is provided for removing any surplus powder from the belt. It will be apparent that the paper recording arrangement of Fig. 8 may be omitted if a permanent record of the electrostatically recorded information is not required.

It is believed that the invention will be fully understood from the foregoing description, and that it will be obvious to those skilled in the art, that many variations and modifications may be made from the preferred embodiments herein shown without departing from the principles and scope of the invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Recording apparatus comprising a cathode ray tube trons toward said target area to excite said element, a,

conductive member disposed externally of and spaced from said tube and adjacent said target area, a source of. direct current potential having one terminal coupled to said source of electrons in the tube the other terminal connectcd to the conductive member, an electrostatically polarizable member positioned intermediate the conductive member and externally of said tube adjacent said target area for storing electrostatic charges corresponding to the excitation produced on the conductive element.

2. Recording apparatus comprising a cathode ray tube having an inner target area, 'a plurality of mutually insulated conductive elements disposed on said inner target area, means including a source of electrons for. projecting a beam of electrons toward said target area. to excite said elements, a conductive member disposed externally of and spaced from said tube and adjacent said target area, a

source of direct current potential having one terminal coupledto said source of electrons. in the tube the'other.

terminal connected to the conductive member, an electrostatically polarizable member positioned intermediate the conductive member and externally of said tube adjacent said target area for storing electrostatic charges corresponding to the excitation produced on the conductive elements.

3. Recording apparatus comprising a cathode ray tube having an inner target area, aplurality of mutually insulated conductive elements disposed on said inner target area, means including a source of electrons for. projecting a beam of electrons toward saidtarget area to excite said elements, a conductive member disposed externally of and spaced from said tube and, adjacent said target area, a

source of direct current potential having onev terminal, coupled to said source of electrons in the tube the other terminal connected to the conductive member, an CIGCtl'O-r statically polarizable member disposed upon saidconductive member, said polarizable member being positioned;

intermediate the conductive member and externally of said tube adjacent said target area for storing electrostatic charges corresponding to the excitation produced on the conductive elements.

4. Recording apparatus comprising-a cathode ray tube having an inner target area, a plurality of mutually insulated conductive elements disposed on said inner target area, means including a source of electrons for projecting a beam of electronstoward said. target area to excite said elements, a conductive member having a predetermined curvature said member being. disposed externally of and spaced from said tube and adjacent said target area, a source of direct current potential having one terminal coupled to said source of electrons in the tube the other terminal connected to the conductive member, an electrostatically polarizable member curved to complement the predetermined curvature and positioned intermediate the conductive member. and externally of said tube adjacent said target area for storing electrostatic charges corresponding to the excitation produced on the conductive elements, said inner target area and said tube adjacent said target area being curved to complement the curvature of said polarizable member.

5. Recording apparatus comprising a cathode ray tube having an inner target area, a plurality of mutually insulated conductive elements disposed on said inner target area, one of said elements forming one plate of a capacitor means including a source of electrons for projecting a beam of electrons toward said target area to excite said elements, a conductive member disposed externally of and spaced from said tube and adjacent said target area, a source of direct current potential having one terminal coupled to said source of electrons in the tube the other terminal connected to the conductivemember,

capacitor an electrostatically polarizable. memberposihaving an inner target area, a plurality of mutually in-.

sulated conductive elements disposed on said inner target area, means including a source of electrons for projecting a character-shaped beam of electrons toward said target area to excite said elements in a pattern reproducing the character shape imparted by the beam, a conductive member disposed externally of and spaced from said tube and adjacent said target area, a source of direct current potential having one terminal coupled to said source of electrons in the tube the other terminal connected to the conductive member, anelectrostatically polarizable member positioned intermediate the conductive member and externally of said tube adjacent said target area, said polarizable member being responsive to said potential source for storing electrostatic charges thereupon corresponding to said pattern produced on. the conductive elements.

7. Recording apparatus comprising a cathode ray tube having an inner target area, a plurality of mutually insulated conductive elements disposed on said inner target area, means including a source of electrons for projecting a beam of electrons toward said target area to excite said elements, a conductive member disposed externally of and spaced from said tube and adjacent said target area, a source of direct current potential having one terminal coupled to said source of electrons in the tube the other terminal connected to the conductive member, a recording medium including an electrostatically polarizable member positioned intermediate the conductive member and externally of said tube adjacent said target area for storing electrostatic charges corresponding to the excitation produced on the conductive elements, said recording medium including means for converting said electrostatic charges stored on said polarizable member to a visible record.

8. Recording apparatus comprising a cathode ray tube having an inner target area, a plurality of mutually insulated conductive elements disposed on said inner target area, means including a source of electrons for projecting a beam of electrons toward said target area to excite said elements, a conductive member disposed externally of and spaced from said tube and adjacent said target area, a source of direct current potential having one terminal coupled to said source of electrons in the tube the other terminal connected to the conductive member, a recording medium including an electrostatically polarizable member positioned intermediate the conductive member and externally of said tube adjacent said target area for storing electrostatic charges corresponding to the excitation produced on the conductive elements, said recording medium including means for converting said electrostatic charges stored on said polarizable member to a visible recordand means for transposing said visual record to a transfer material for recordation.

9. Recording apparatus in accordance with claim 7 wherein said polarizable member is a continuous belt polarizable member.

References Cited in the file of this patent UNITED STATES PATENTS 2,015,570 Sabbah et al. Sept. 24, 1935 2,143,214 Selenyi Jan. 10, 1939 2,200,741 Gray May 14, 1940 2,273,793 Ekstrand Feb. 17, 1942 2,283,383 McNaney May 19, 1942 2,301,199 Bruce et al. Nov. 10, 1942 2,449,752 Ross Sept. 21, 1948 2,624,652 Carlson Jan. 5, 1953 OTHER REFERENCES Popular Mechanics,"-July 1952-; page 136; 

